Re: [RFC PATCH v2] Add ARM cpu topology definition

From: Vincent Guittot
Date: Wed Jun 22 2011 - 08:21:01 EST


On 22 June 2011 12:14, Amit Kucheria <amit.kucheria@xxxxxxxxxx> wrote:
> Some nits below.
>
> After you fix them, you can add a
> Reviewed-by: Amit Kucheria <amit.kucheria@xxxxxxxxxx>
>
> On 11 Jun 20, Vincent Guittot wrote:
>> The affinity between ARM processors is defined in the MPIDR register.
>> We can identify which processors are in the same cluster,
>> and which ones have performance interdependency.We can define the
>                                                 ^^ space between full-stop
>                                                 and next word
>> cpu topology of ARM platform, which is used by sched_mc and sched_smt.
>                                ^^^^^^^^ change to 'that is then'
>> The default state of sched_mc and sched_smt config is disable.
>
> Change to "sched_mc and sched_smt is disabled by default"
>
>> When enable, the behavior of the scheduler can be modified with
>             ^ enabled
>> sched_mc_power_savings and sched_smt_power_savings sysfs interfaces.
>>
>> Changes since v1 :
>> * Update the commit message
>> * Add read_cpuid_mpidr in arch/arm/include/asm/cputype.h
>> * Modify header of arch/arm/kernel/topology.c
>> * Modify tests and manipulation of MPIDR's bitfields
>> * Modify the place and dependancy of the config
>> * Modify Noop functions
>>
>> Signed-off-by: Vincent Guittot <vincent.guittot@xxxxxxxxxx>
>> ---
>>  arch/arm/Kconfig                |   25 +++++++
>>  arch/arm/include/asm/cputype.h  |    6 ++
>>  arch/arm/include/asm/topology.h |   33 +++++++++
>>  arch/arm/kernel/Makefile        |    1 +
>>  arch/arm/kernel/smp.c           |    6 ++
>>  arch/arm/kernel/topology.c      |  145 +++++++++++++++++++++++++++++++++++++++
>>  6 files changed, 216 insertions(+), 0 deletions(-)
>>  create mode 100644 arch/arm/kernel/topology.c
>>
>> diff --git a/arch/arm/Kconfig b/arch/arm/Kconfig
>> index 9adc278..c7b4ff9 100644
>> --- a/arch/arm/Kconfig
>> +++ b/arch/arm/Kconfig
>> @@ -1344,6 +1344,31 @@ config SMP_ON_UP
>>
>>         If you don't know what to do here, say Y.
>>
>> +config ARM_CPU_TOPOLOGY
>> +     bool "Support cpu topology definition"
>> +     depends on SMP && CPU_V7
>> +     default y
>> +     help
>> +       Support ARM cpu topology definition. The MPIDR register defines
>> +       affinity between processors which is used to set the cpu
>                                              ^^^^^^^^^^^^^^^^^ change to 'which is then
>                                              used to describe the'
>> +       topology of an ARM System.
>> +
>> +config SCHED_MC
>> +     bool "Multi-core scheduler support"
>> +     depends on ARM_CPU_TOPOLOGY
>> +     help
>> +       Multi-core scheduler support improves the CPU scheduler's decision
>> +       making when dealing with multi-core CPU chips at a cost of slightly
>> +       increased overhead in some places. If unsure say N here.
>> +
>> +config SCHED_SMT
>> +     bool "SMT scheduler support"
>> +     depends on ARM_CPU_TOPOLOGY
>> +     help
>> +       Improves the CPU scheduler's decision making when dealing with
>> +       MultiThreading at a cost of slightly increased overhead in some
>> +       places. If unsure say N here.
>> +
>>  config HAVE_ARM_SCU
>>       bool
>>       depends on SMP
>> diff --git a/arch/arm/include/asm/cputype.h b/arch/arm/include/asm/cputype.h
>> index cd4458f..cb47d28 100644
>> --- a/arch/arm/include/asm/cputype.h
>> +++ b/arch/arm/include/asm/cputype.h
>> @@ -8,6 +8,7 @@
>>  #define CPUID_CACHETYPE      1
>>  #define CPUID_TCM    2
>>  #define CPUID_TLBTYPE        3
>> +#define CPUID_MPIDR  5
>>
>>  #define CPUID_EXT_PFR0       "c1, 0"
>>  #define CPUID_EXT_PFR1       "c1, 1"
>> @@ -70,6 +71,11 @@ static inline unsigned int __attribute_const__ read_cpuid_tcmstatus(void)
>>       return read_cpuid(CPUID_TCM);
>>  }
>>
>> +static inline unsigned int __attribute_const__ read_cpuid_mpidr(void)
>> +{
>> +     return read_cpuid(CPUID_MPIDR);
>> +}
>> +
>>  /*
>>   * Intel's XScale3 core supports some v6 features (supersections, L2)
>>   * but advertises itself as v5 as it does not support the v6 ISA.  For
>> diff --git a/arch/arm/include/asm/topology.h b/arch/arm/include/asm/topology.h
>> index accbd7c..63a7454 100644
>> --- a/arch/arm/include/asm/topology.h
>> +++ b/arch/arm/include/asm/topology.h
>> @@ -1,6 +1,39 @@
>>  #ifndef _ASM_ARM_TOPOLOGY_H
>>  #define _ASM_ARM_TOPOLOGY_H
>>
>> +#ifdef CONFIG_ARM_CPU_TOPOLOGY
>> +
>> +#include <linux/cpumask.h>
>> +
>> +struct cputopo_arm {
>> +     int thread_id;
>> +     int core_id;
>> +     int socket_id;
>> +     cpumask_t thread_sibling;
>> +     cpumask_t core_sibling;
>> +};
>> +
>> +extern struct cputopo_arm cpu_topology[NR_CPUS];
>> +
>> +#define topology_physical_package_id(cpu)    (cpu_topology[cpu].socket_id)
>> +#define topology_core_id(cpu)                (cpu_topology[cpu].core_id)
>> +#define topology_core_cpumask(cpu)   (&(cpu_topology[cpu].core_sibling))
>> +#define topology_thread_cpumask(cpu) (&(cpu_topology[cpu].thread_sibling))
>
> These #defines are not used anywhere.

They are used in topology.c driver and sched.c

>
>> +#define mc_capable() (cpu_topology[0].socket_id != -1)
>> +#define smt_capable()        (cpu_topology[0].thread_id != -1)
>
> Neither are these.

They are used in sched.c

>
>> +void init_cpu_topology(void);
>> +void store_cpu_topology(unsigned int cpuid);
>> +const struct cpumask *cpu_coregroup_mask(unsigned int cpu);
>> +
>> +#else
>> +
>> +static inline void init_cpu_topology(void) { };
>> +static inline void store_cpu_topology(unsigned int cpuid) { };
>> +
>> +#endif
>> +
>>  #include <asm-generic/topology.h>
>>
>>  #endif /* _ASM_ARM_TOPOLOGY_H */
>> diff --git a/arch/arm/kernel/Makefile b/arch/arm/kernel/Makefile
>> index a5b31af..816a481 100644
>> --- a/arch/arm/kernel/Makefile
>> +++ b/arch/arm/kernel/Makefile
>> @@ -61,6 +61,7 @@ obj-$(CONFIG_IWMMXT)                += iwmmxt.o
>>  obj-$(CONFIG_CPU_HAS_PMU)    += pmu.o
>>  obj-$(CONFIG_HW_PERF_EVENTS) += perf_event.o
>>  AFLAGS_iwmmxt.o                      := -Wa,-mcpu=iwmmxt
>> +obj-$(CONFIG_ARM_CPU_TOPOLOGY)  += topology.o
>>
>>  ifneq ($(CONFIG_ARCH_EBSA110),y)
>>    obj-y              += io.o
>> diff --git a/arch/arm/kernel/smp.c b/arch/arm/kernel/smp.c
>> index 344e52b..3e8dc3b 100644
>> --- a/arch/arm/kernel/smp.c
>> +++ b/arch/arm/kernel/smp.c
>> @@ -31,6 +31,7 @@
>>  #include <asm/cacheflush.h>
>>  #include <asm/cpu.h>
>>  #include <asm/cputype.h>
>> +#include <asm/topology.h>
>>  #include <asm/mmu_context.h>
>>  #include <asm/pgtable.h>
>>  #include <asm/pgalloc.h>
>> @@ -268,6 +269,9 @@ static void __cpuinit smp_store_cpu_info(unsigned int cpuid)
>>       struct cpuinfo_arm *cpu_info = &per_cpu(cpu_data, cpuid);
>>
>>       cpu_info->loops_per_jiffy = loops_per_jiffy;
>> +
>> +     store_cpu_topology(cpuid);
>> +
>>  }
>>
>>  /*
>> @@ -354,6 +358,8 @@ void __init smp_prepare_cpus(unsigned int max_cpus)
>>  {
>>       unsigned int ncores = num_possible_cpus();
>>
>> +     init_cpu_topology();
>> +
>>       smp_store_cpu_info(smp_processor_id());
>>
>>       /*
>> diff --git a/arch/arm/kernel/topology.c b/arch/arm/kernel/topology.c
>> new file mode 100644
>> index 0000000..dc9e4be
>> --- /dev/null
>> +++ b/arch/arm/kernel/topology.c
>> @@ -0,0 +1,145 @@
>> +/*
>> + * arch/arm/kernel/topology.c
>> + *
>> + * Copyright (C) 2011 Linaro Limited.
>> + * Written by: Vincent Guittot
>> + *
>> + * based on arch/sh/kernel/topology.c
>> + *
>> + * This file is subject to the terms and conditions of the GNU General Public
>> + * License.  See the file "COPYING" in the main directory of this archive
>> + * for more details.
>> + */
>> +
>> +#include <linux/cpu.h>
>> +#include <linux/cpumask.h>
>> +#include <linux/init.h>
>> +#include <linux/percpu.h>
>> +#include <linux/node.h>
>> +#include <linux/nodemask.h>
>> +#include <linux/sched.h>
>> +
>> +#include <asm/cputype.h>
>> +#include <asm/topology.h>
>> +
>> +#define MPIDR_SMP_BITMASK (0x3 << 30)
>> +#define MPIDR_SMP_VALUE (0x2 << 30)
>> +
>> +#define MPIDR_MT_BITMASK (0x1 << 24)
>> +
>> +#define MPIDR_LEVEL0_MASK 0x3
>
> Perhaps add a comment reflecting the discussion on IRC. For Cortex-A9, only
> 2 bits are supported for LEVEL0 and 4 bits for LEVEL1. In the future, each of
> the LEVELS can use all 8 bits.
>

ok

>> +#define MPIDR_LEVEL0_SHIFT 0
>> +
>> +#define MPIDR_LEVEL1_MASK 0xF
>> +#define MPIDR_LEVEL1_SHIFT 8
>> +
>> +#define MPIDR_LEVEL2_MASK 0xFF
>> +#define MPIDR_LEVEL2_SHIFT 16
>> +
>> +struct cputopo_arm cpu_topology[NR_CPUS];
>> +
>> +const struct cpumask *cpu_coregroup_mask(unsigned int cpu)
>> +{
>> +     return &(cpu_topology[cpu].core_sibling);
>> +}
>> +
>> +/*
>> + * store_cpu_topology is called at boot when only one cpu is running
>> + * and with the mutex cpu_hotplug.lock locked, when several cpus have booted,
>> + * which prevents simultaneous write access to cpu_topology array
>> + */
>> +void store_cpu_topology(unsigned int cpuid)
>> +{
>> +     struct cputopo_arm *cpuid_topo = &(cpu_topology[cpuid]);
>> +     unsigned int mpidr;
>> +     unsigned int cpu;
>> +
>> +     /* If the cpu topology has been already set, just return */
>> +     if (cpuid_topo->core_id != -1)
>> +             return;
>> +
>> +     mpidr = read_cpuid_mpidr();
>> +
>> +     /* create cpu topology mapping */
>> +     if ((mpidr & MPIDR_SMP_BITMASK) == MPIDR_SMP_VALUE) {
>> +             /*
>> +              * This is a multiprocessor system
>> +              * multiprocessor format & multiprocessor mode field are set
>> +              */
>> +
>> +             if (mpidr & MPIDR_MT_BITMASK) {
>> +                     /* core performance interdependency */
>> +                     cpuid_topo->thread_id = ((mpidr >> MPIDR_LEVEL0_SHIFT)
>> +                             & MPIDR_LEVEL0_MASK);
>> +                     cpuid_topo->core_id =  ((mpidr >> MPIDR_LEVEL1_SHIFT)
>> +                             & MPIDR_LEVEL1_MASK);
>> +                     cpuid_topo->socket_id = ((mpidr >> MPIDR_LEVEL2_SHIFT)
>> +                             & MPIDR_LEVEL2_MASK);
>> +             } else {
>> +                     /* normal core interdependency */
>                           ^^^^^^ Normal or No?

ARM ARM says "largely independent". I can use this description

>
>> +                     cpuid_topo->thread_id = -1;
>> +                     cpuid_topo->core_id = ((mpidr >> MPIDR_LEVEL0_SHIFT)
>> +                             & MPIDR_LEVEL0_MASK);
>> +                     cpuid_topo->socket_id = ((mpidr >> MPIDR_LEVEL1_SHIFT)
>> +                             & MPIDR_LEVEL1_MASK);
>> +             }
>> +     } else {
>> +             /*
>> +              * This is an uniprocessor system
>> +              * we are in multiprocessor format but uniprocessor system
>> +              * or in the old uniprocessor format
>> +              */
>
> These are 3 different conditions, I think. Separate with commas.

we are either in the "multiprocessor register format but an uniprocessor"
or in the "old uniprocessor register format"

>
>> +
>> +             cpuid_topo->thread_id = -1;
>> +             cpuid_topo->core_id = 0;
>> +             cpuid_topo->socket_id = -1;
>> +     }
>> +
>> +     /* update core and thread sibling masks */
>> +     for_each_possible_cpu(cpu) {
>> +             struct cputopo_arm *cpu_topo = &(cpu_topology[cpu]);
>> +
>> +             if (cpuid_topo->socket_id == cpu_topo->socket_id) {
>> +                     cpumask_set_cpu(cpuid, &cpu_topo->core_sibling);
>> +                     if (cpu != cpuid)
>> +                             cpumask_set_cpu(cpu,
>> +                                     &cpuid_topo->core_sibling);
>> +
>> +                     if (cpuid_topo->core_id == cpu_topo->core_id) {
>> +                             cpumask_set_cpu(cpuid,
>> +                                     &cpu_topo->thread_sibling);
>> +                             if (cpu != cpuid)
>> +                                     cpumask_set_cpu(cpu,
>> +                                             &cpuid_topo->thread_sibling);
>> +                     }
>> +             }
>> +     }
>> +     smp_wmb();
>> +
>> +     printk(KERN_INFO "cpu %u : thread %d cpu %d, socket %d, mpidr %x\n",
>> +             cpuid, cpu_topology[cpuid].thread_id,
>> +             cpu_topology[cpuid].core_id,
>> +             cpu_topology[cpuid].socket_id, mpidr);
>> +
>> +}
>> +
>> +/*
>> + * init_cpu_topology is called at boot when only one cpu is running
>> + * which prevent simultaneous write access to cpu_topology array
>> + */
>> +void init_cpu_topology(void)
>> +{
>> +     unsigned int cpu;
>> +
>> +     /* init core mask */
>> +     for_each_possible_cpu(cpu) {
>> +             struct cputopo_arm *cpu_topo = &(cpu_topology[cpu]);
>> +
>> +             cpu_topo->thread_id = -1;
>> +             cpu_topo->core_id =  -1;
>> +             cpu_topo->socket_id = -1;
>> +             cpumask_clear(&cpu_topo->core_sibling);
>> +             cpumask_clear(&cpu_topo->thread_sibling);
>> +     }
>> +     smp_wmb();
>> +}
>> --
>> 1.7.4.1
>>
>
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